Heat recovery apparatus

ABSTRACT

A heat recovery apparatus has an evaporating part for evaporating an internal fluid and a condensing part for condensing the internal fluid evaporated in the evaporating part. The evaporating part and the condensing part are in communication with each other through a looped passage for circulating the internal fluid therethrough. The evaporating part has evaporating heat pipes and evaporating fins. Each evaporating heat pipes has flange portions at longitudinal ends thereof. The flange portions project in a direction perpendicular to a longitudinal direction of the evaporating heat pipe and have a tubular shape. The evaporating heat pipes and the evaporating fins are alternately stacked and brazed, and the flange portions of the adjacent evaporating heat pipes are coupled to and brazed to each other such that communication portions are provided by the coupled flange portions and longitudinal ends of the evaporating heat pipes.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2006-33429 filed on Feb. 10, 2006, the disclosures of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a heat recovery apparatus, which is for example used in a vehicle.

BACKGROUND OF THE INVENTION

It is known to use a principle of heat pipe in a heat exchanger as disclosed in Japanese Unexamined Patent Publication No. 4-45393, for example. In this heat exchanger, an evaporating part and a condensing part are disposed on an enclosed circulation passage. The enclosed circulation passage forms a closed loop. An evaporable and condensable heat transfer fluid is enclosed in the enclosed circulation passage.

The evaporating part performs heat exchange between the heat transfer fluid and an external fluid, thereby evaporating the heat transfer fluid. The condensing part is arranged at a position higher than the evaporating part. The condensing part performs heat exchange between the heat transfer fluid that has been evaporated in the evaporating part and an external fluid, thereby condensing the heat transfer fluid.

Also, it is proposed to use such a looped heat pipe heat exchanger as a heat recovery apparatus in a vehicle. For example, an evaporating part is disposed in an exhaust pipe of an engine for recovering heat of an exhaust gas, and the heat may be used for a warm-up operation. FIG. 7 shows an example of the heat recovery apparatus used in a vehicle. The heat recovery apparatus has an evaporating part J1 and a condensing part J2 both including heat pipes J3. Longitudinal ends of the heat pipes J3 are coupled to headers (communication portions) J6. This heat recovery device is for example manufactured in a following manner.

First, components J3, J4, J6 are assembled. For example, ends of the heat pipes J3 are inserted to slit holes of the headers J6 and fins J4 a, J4 b are interposed between the heat pipes J3. Then, this assembly is preliminarily fixed with fixing means such as jigs by applying loads in two directions. Specifically, the loads are applied in a direction perpendicular to the heat pipes J3 for fixing the heat pipes J3 and the fins J4 a, J4 b and in a direction parallel to the heat pipes J3 for fixing the headers J6 to the heat pipes J3. In this condition, the assembly is heated by heating means, so the components J3, J4, J6 are integrally brazed.

The above components are for example made of stainless having high-corrosion resistance. Because the evaporating part J1 is subjected to high temperature in the exhaust pipe, nickel alloy is used as a brazing material for brazing. However, because a melting point of the nickel alloy is high, high brazing temperature is required. Therefore, it will be difficult to apply the loads in two directions under such a high brazing temperature during brazing.

Further, the evaporating part J1 thermally expands due to the high temperature in the exhaust pipe. In this construction, thermal stress due to thermal expansion and contraction of the heat pipes J3 (arrows X) and thermal expansion and contraction of the headers J6 (arrows Y) is concentrated to joining portions between the heat pipes J3 and the headers J6. This will cause breakages of the joining portions.

SUMMARY OF THE INVENTION

The present invention is made in view of the foregoing matter, and it is an object of the present invention to provide a heat recovery apparatus with improved manufacturability. It is another object of the present invention to provide a heat recovery apparatus capable of reducing thermal stress.

According to an aspect of the present invention, a heat recovery apparatus has an evaporating part and a condensing part. The evaporating part and the condensing part are disposed on a looped passage through which an internal fluid circulates. The evaporating part performs heat exchange between the internal fluid and a first fluid, thereby to evaporate the internal fluid. The condensing part performs heat exchange between the internal fluid evaporated in the evaporating part and a second fluid having a temperature lower than a temperature of the first fluid, thereby to condense the internal fluid.

The evaporating part has a plurality of evaporating heat pipes and evaporating fins. Each of the evaporating heat pipes has flange portions projecting from its longitudinal ends in a direction perpendicular to a longitudinal direction of the evaporating heat pipe. Each flange portion has a tubular shape. The evaporating heat pipes and the evaporating fins are alternately stacked and brazed in a direction perpendicular to the longitudinal direction of the evaporating heat pipes, and the flange portions of the adjacent evaporating heat pipes are coupled to and brazed to each other such that evaporating communication portions are provided by the flange portions and the longitudinal ends of the evaporating heat pipes.

In this construction, since the communication portions are formed by coupling the flange portions of the evaporating heat pipes, the heat recovery apparatus is brazed in a condition being held in one direction, i.e., in a direction perpendicular to the longitudinal direction of the evaporating heat pipes. Therefore, the heat recovery apparatus is easily assembled and brazed

According to a second aspect of the present invention, the evaporating part and the condensing part are disposed close to each other and coupled through coupling members. Thus, a compact heat recovery apparatus is provided. For example, the evaporating part and the condensing part are coupled such that the evaporating heat pipes and condensing heat pipes are parallel to each other. In this case, the evaporating part and the condensing part are integrally brazed. Thus, manufacturability improves.

According to a third aspect of the present invention, the evaporating part has stress absorbing portions in communication portions. Because the evaporating part is placed in the flow of the first fluid having high temperature, it causes thermal expansion. Since the thermal expansion in a direction perpendicular to the longitudinal direction of the evaporating heat pipes is absorbed by the stress absorbing portion, thermal stress is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic cross-sectional view of a heat recovery apparatus according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of an evaporating heat pipe of the heat recovery apparatus according to the first embodiment;

FIG. 3 is a schematic cross-sectional view of a heat recovery apparatus according to a second embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view of an evaporating communication portion of a heat recovery apparatus according to a third embodiment of the present invention;

FIG. 5 is a cross-sectional view of an evaporating heat pipe of a heat recovery apparatus according to a fourth embodiment of the present invention;

FIG. 6 is a cross-sectional view of an evaporating communication portion of a heat recovery apparatus according to another embodiment of the present invention; and

FIG. 7 is a schematic cross-sectional view of a heat recovery apparatus as a related art.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. A heat recovery apparatus is for example mounted to a vehicle for collecting exhaust heat of an exhaust gas from an exhaust system of a vehicle engine and using the collected heat as a heat source for an air conditioning system and the like.

As shown in FIG. 1, the heat recovery apparatus has an evaporating part 1 and a condensing part 2 arranged next to each other. The evaporating part 1 is disposed in an evaporating case 100 that is arranged in an exhaust pipe (not shown) of the engine. The evaporating part 1 performs heat exchange between the exhaust gas and a heat transfer fluid (internal fluid), thereby evaporating the heat transfer fluid.

The condensing part 2 is disposed outside of the exhaust pipe. The condensing part 2 is disposed in a condensing case 200 that is disposed in a cooling water passage (not shown) through which an engine cooling water circulates. The condensing part 2 performs heat exchange between the heat transfer fluid that has been evaporated in the evaporating part 1 and the engine cooling water, thereby condensing the heat transfer fluid.

Next, a structure of the evaporating part 1 will be described. The evaporating part 1 has a first heat exchanging section 5 a. The first heat exchanging section 5 a includes evaporating heat pipes 3 a and evaporating fins 4 a. The evaporating fins 4 a are for example corrugated fins and joined to outer surfaces of the evaporating heat pipes 3 a.

Each of the evaporating heat pipes 3 a has a flat pipe shape. The evaporating heat pipes 3 a are arranged parallel to each other and extend in a vertical direction (arrow A1 in FIG. 1). FIG. 2 shows a cross-section of the evaporating heat pipe 3 a defined in a direction perpendicular to a longitudinal direction of the evaporating heat pipe 3 a.

Each evaporating heat pipe 3 a is arranged such that a longitudinal axis of the cross-section is parallel to a flow direction of the exhaust gas. That is, the up and down direction of FIG. 2 corresponds to the flow direction of the exhaust gas. In FIG. 1, a direction perpendicular to a paper plane corresponds to the flow direction of the exhaust gas.

The evaporating part 1 has evaporating headers 6 a (evaporating communication portions) at the longitudinal ends of the evaporating heat pipes 3 a. The evaporating headers 6 a extend in a direction that the heat pipes 3 a are stacked (arrow A2). The evaporating headers 6 a are in communication with all of the heat pipes 3 a.

Here, one of the evaporating headers 6 a, which is arranged at the upper ends of the heat pipes 3 a, is referred to as a first evaporating header 61 a. The other evaporating header 6 b, which is arranged at the lower ends of the heat pipes 3 a, is referred to as a first return-flow header 62 a.

As shown in FIG. 2, each evaporating heat pipe 3 a is constructed of a pair of formed plates 31 a, 32 a as evaporating heat pipe members, each having a substantially plate shape and a substantially U-shaped cross-section. The formed plates 31 a, 32 a are opposed such that an evaporating pipe space is defined between them.

Further, each of the formed plates 31 a, 32 a has a pair of evaporating flange portions 33 a at longitudinal ends thereof. Each evaporating flange portion 33 a projects in an outward direction of the heat pipe 3 a. The flange portion 33 a has a substantially tubular shape and defines an opening at an end. The formed plates 31 a, 32 a are opposed such that the flange portions 33 a project in opposite directions.

A diameter of the opening of the flange portion 33 a of one of the pair of formed plates 31 a, 32 a is larger than a diameter of the opening of the flange portion 33 a of the other of the pair of formed plates 31 a, 32 a. Thus, the end of the flange portion 33 a of one heat pipe 3 a is received in and engaged with the end of the flange portion 33 a of the adjacent heat pipe 3 a.

Next, a structure of the condensing part 2 will be described. As shown in FIG. 1, the condensing part 2 has a second heat exchanging section 5 b. The second heat exchanging section 5 b includes condensing heat pipes 3 b and condensing fins 4 b. The condensing fins 4 b are for example straight fins and joined to outer surfaces of the condensing heat pipes 3 b.

Each of the condensing heat pipes 3 b has a flat pipe shape, similar to the evaporating heat pipes 3 a. The condensing heat pipe 3 b is disposed such that the major axis in its cross-section defined perpendicular to the longitudinal direction is parallel to a flow direction of cooling water. Further, the condensing heat pipes 3 b are arranged parallel to each other and extend in the vertical direction (arrow A1).

The condensing part 2 further has condensing headers 6 b at longitudinal ends of the condensing heat pipes 3 b as condensing communication portions. The condensing headers 6 b extend in the direction (arrow A2) that the condensing heat pipes 3 b are arranged and are in communication with all of the condensing heat pipes 3 b.

One of the condensing headers 6 b, which is arranged at the upper ends of the condensing heat pipes 3 b, is referred to as a second evaporating header 61 b. The other of the condensing headers 6 b, which is arranged at lower ends of the condensing heat pipes 3 b, is referred to as a second return-flow header 62 b.

Similar to the evaporating heat pipes 3 a, each of the condensing heat pipes 3 b is constructed of a pair of formed plates 31 b, 32 b as condensing heat pipe members. The condensing heat pipes 3 b have the similar cross-section as the evaporating heat pipes 3 a, as shown in FIG. 2. Each of the formed plates 31 b, 32 b has a substantially plate shape and a substantially U-shaped cross-section. The formed plates 31 b, 32 b are opposed such that a condensing pipe space is defined between them.

Further, each of the formed plates 31 b, 32 b has a pair of condensing flange portions 33 b at longitudinal ends thereof. Each condensing flange portion 33 b projects in an outward direction of the heat pipe 3 b. The flange portion 33 b has a substantially tubular shape and defines an opening at its end. The formed plates 31 a, 32 b are opposed such that the flange portions 33 b project in opposite directions.

A diameter of the opening of the flange portion 33 b of one of the pair of formed plates 31 b, 32 b is larger than a diameter of the opening of the flange portion 33 a of the other of the pair of formed plates 31 b, 32 b. Thus, the end of the flange portion 33 b of one heat pipe 3 b is received in and engaged with the end of the flange portion 33 b of the adjacent heat pipe 3 b.

Further, inner fins 34 are provided in the evaporating heat pipes 3 a and the condensing heat pipes 3 b for increasing heat transfer areas so as to improve heat exchange efficiency, as shown in FIG. 2.

The evaporating headers 6 a and the condensing headers 6 b are in communication with each other through coupling pipes (coupling members) 7 each having a pipe shape. The evaporating and condensing heat pipes 3 a, 3 b and the evaporating and condensing headers 6 a, 6 b and the coupling pipes 7 form an enclosed looped passage. The evaporable and condensable heat transfer fluid such as water or alcohol is enclosed in the enclosed passage.

Since the coupling pipes 7 are provided between the evaporating headers 6 a and the condensing headers 6 b, a clearance 8 is remained between the evaporating part 1 (evaporating case 100) and the condensing part 2 (condensing case 200). The evaporating part 1 and the condensing part 2 are thermally insulated through the clearance 8.

Next, a method of manufacturing the heat recovery apparatus will be described. First, the evaporating formed plates 31 a, 32 a are paired. The paired formed plates 31 a, 32 a and the evaporating fins 4 are alternately stacked in the direction perpendicular to the longitudinal direction of the evaporating heat pipes 3 a in the evaporating case 100. With this, the ends of the evaporating flange portions 33 a of the adjacent evaporating heat pipes 3 a are engaged with each other to make communication with each other. Thus, the evaporating headers 6 a are constructed by the coupled evaporating flange portions 33 a and the longitudinal ends of the evaporating heat pipes 3 a.

Likewise, the condensing formed plates 31 b, 32 b are paired. The paired formed plates 31 b, 32 b and the condensing fins 4 b are alternately stacked in the direction perpendicular to the longitudinal direction of the condensing heat pipes 3 b in the condensing case 200. With this, the ends of the condensing flange portions 33 b of the adjacent condensing heat pipes 3 b are engaged with each other to make communication with each other. Thus, the condensing headers 6 b are constructed by the coupled condensing flange portions 33 b and the longitudinal ends of the condensing heat pipes 3 b.

Then, the coupling pipes 7 are coupled between the evaporating headers 6 a and the condensing headers 6 b. Accordingly, all components 100, 200, 31 a, 32 a, 31 b, 32 b, 4 a, 4 b are stacked in one direction (stacking direction, arrow A2).

Thereafter, the stacked components are held and fixed by a jig (not shown) in the stacking direction such that a predetermined load is applied in the stacking direction. In this condition, the stacked components are placed in furnace and heated. Accordingly, the components are integrally brazed.

Namely, joining portions between the heat pipes 3 a, 3 b, the fins 4 a, 4 b, the headers 6 a, 6 b and the coupling pipes 7 are brazed. In this case, the formed plates 31 a, 32 a, 31 b, 32 b are brazed at the same time as brazing with other components. In other words, the heat pipes 3 a, 3 b are formed at the same time as integrally brazing. In the embodiment, all of the components are made of stainless, and a nickel alloy is used as a brazing material.

As described above, the heat pipes 3 a, 3 b are formed by arranging the formed plates 31 a, 32 a, 31 b, 32 b in pairs and brazing thereof, and the heat pipes 3 a, 3 b and the fins 4 a, 4 b are alternately stacked. Therefore, the preliminarily assembled components are merely held in one direction during the brazing. Namely, the load is only applied in the stacking direction during the brazing. As such, it is easy to assemble and braze all components of the heat recovery apparatus.

In this embodiment, the evaporating part 1 and the condensing part 2 are arranged next to each other. For example, the evaporating part 1 and the condensing part 2 are arranged such that the evaporating headers 6 a and the condensing headers 6 b are aligned with each other. Therefore, the heat recovery apparatus is reduced in size and easily mounted to the vehicle. Further, since the evaporating part 1 and the condensing part 2 are brazed at the same time, the manufacturing steps are reduced.

Second Embodiment

A second embodiment will be described with reference to FIG. 3. Here, like components are denoted by like reference numerals, and a description thereof will not be repeated.

As shown in FIG. 3, the evaporating formed plate 31 a, which is one of the paired formed plates, has a first bellows portion 9 as a stress absorbing portion to extend from the flange portion 33 a. The first bellows portion 9 is integrally formed with the flange portion 33 a. The end of the first bellows portion 9 defines an opening and is configured to be engaged with the end of the flange portion 33 a of the formed plate 32 a of the adjacent evaporating heat pipe 3 a.

The first bellows portion 9 is formed with first bulges 91. In the example of FIG. 3, two first bulges 91 are formed. The first bulges 91 can expand and contract in a radial direction of the first bellows portion 9. Each of the first bulges 91 projects in a radial outward direction and extends entirely in a circumferential direction of the first bellows portion 9. As such, the first bellows portion 9 is in a form of bellows and can expand and contract, i.e., is elastic in the stacking direction (arrow A2) of the evaporating heat pipes 3 a.

Further, the evaporating part 1 and the condensing part 2 are connected through bellows coupling pipes having second bellows portions 10 as stress absorbing portions, instead of the straight coupling pipes 7 of the first embodiment. The bellows coupling pipes are formed as separate parts and engaged with the first bellows portion 9 of the evaporating heat pipe 3 a, which is disposed adjacent to the condensing part 2, and the flange portion 33 b of the condensing heat pipe 3 b, which is disposed adjacent to the evaporating part 1.

Each of the second bellows portions 10 is formed with second bulges 101. In the example of FIG. 3, three second bulges 101 are formed. Each of the second bulges 101 projects in a radial outward direction and entirely extends in a circumferential direction of the second bellows portion 10. The second bulges 101 can expand and contract in a radial direction of the second bellows portion 10. Namely, the bellows coupling pipe is in a form of bellows and can expand and contract, i.e., is elastic in the stacking direction (arrow A2) of the evaporating heat pipes 3 a.

Since the number of the bulges 101 of each second bellows portion 10 is greater than that of the bulges 91 of each first bellows portion 9, the second bellows portion 10 is more elastic than the first bellows portion 9.

Next, an operation of heat recovery apparatus will be described.

Since the evaporating part 1 is disposed in the exhaust pipe of the engine (not shown), it is subjected to high temperature at times. Therefore, the evaporating heat pipes 3 a and the evaporating headers 6 a are largely expand and contract. As the first bellows portions 9 are elastic in the stacking direction of the evaporating heat pipes 3 a, the thermal expansion in the stacking direction of the evaporating heat pipes 3 a is absorbed. Further, as the first bulge portions 91 expand and contract in the longitudinal direction of the evaporating heat pipes 3 a, the thermal expansion in the longitudinal direction of the evaporating heat pipes 3 a is absorbed.

The evaporating part 1 is highly heated by the exhaust gas, while the condensing part 2 is cooled by the engine cooling water to a relative low temperature. Therefore, there is a large temperature difference between the evaporating part 1 and the condensing part 2, causing thermal stress largely between the evaporating part 1 and the condensing part 2. In this case, as the second bellows portions 10 are elastic, which is more elastic than the first bellows portions 9, the thermal stress due to the temperature difference is absorbed.

In the second embodiment as described above, the thermal expansion in the stacking direction of the evaporating heat pipes 3 a is absorbed by the first bellows portions 9, and the thermal expansion in the longitudinal direction of the evaporating heat pipes 3 a is absorbed by the first bulges 91 of the first bellows portions 9. Therefore, the thermal stress to the joining portions of the respective components is reduced.

In addition, the thermal stress between the evaporating part 1 and the condensing part 2 due to the temperature difference between them is effectively absorbed by the second bellows portions 10, which have elasticity higher than the first bellows portions 9.

Third Embodiment

A third embodiment will be described with reference to FIG. 4. Like components are denoted by like reference numerals, and a description thereof will not be repeated.

As shown in FIG. 4, the first bellows portions 9 are formed as separate parts. The ends of each first bellows portion 9 are engaged with the ends of the flange portions 33 a of the evaporating formed plates 31 a, 32 a, respectively. Also in this embodiment, similar advantageous effects are provided.

In addition, since the first bellows portions 9 are formed separate from the evaporating formed plates 31 a, 32 a, the first bulges 91 are more easily formed, as compared with the case in which the first bellows portions 9 are integrally formed with the flange portions 33 a of the formed plates 31 a, 32 a.

Fourth Embodiment

A fourth embodiment will be described with reference to FIGS. 4 and 5. Like components are denoted by like reference numerals, and a description thereof will not be repeated.

The structure of the formed plates 31 a, 32 a, 31 b, 32 b can be modified. As shown in FIG. 5, each of the evaporating formed plates 31 a, 32 a is formed by bending a plate into a substantially U-shape. Each formed plate 31 a, 32 a has a flat portion 310 a, 320 a and a pair of side portions 311 a, 321 a at sides of the flat portions 310 a, 320 a. The side portions 311 a, 321 a are substantially perpendicular to the flat portion 310 a, 320 a.

A distance of the side portions 311 a of the evaporating formed plate 31 a is smaller than a distance of the side portions 321 a of the evaporating formed plate 32 a. Thus, the evaporating plates 31 a, 32 a are engaged such that the side portions 311 a overlap with inner surfaces of the side portions 321 a.

The formed plates 31 b, 32 b of the condensing heat pipes 3 b have flat portions 310 b, 320 b and side portions 311 b, 321 b and engaged similar to the formed plates 31 a, 32 a of the evaporating heat pipes 3 a. Also in this embodiment, similar advantageous effects are provided.

Other Embodiments

In the second embodiment, two bulges 91 are formed on each first bellows portion 9. However, the number of the bulges 91 is not limited to two. For example, the first bellows portion 9 has one bulge 91, as shown in FIG. 6. Also, it is not always necessary that the heat recovery apparatus has both of the first bellows portions 9 and the second bellows portions 10. For example, the second bellows portion 10 may be eliminated depending on a use condition.

In the above embodiments, the evaporating headers 61 a, 61 b and the return-flow headers 62 a, 62 b have the same dimension in the longitudinal direction of the heat pipes 3 a, 3 b. However, the evaporating headers 61 a, 61 b and the return-flow headers 62 a, 62 b may have different dimensions as long as the dimension of the evaporating headers 61 a, 61 b is larger than that of the return-flow headers 62 a, 62 b.

In the above embodiments, the inner fins 34 are provided in the heat pipes 3 a, 3 b. However, the inner fins 34 may be eliminated.

Further, it is not always necessary that the evaporating part 1 and the condensing part 2 are arranged close to each other. The evaporating part 1 and the condensing part 2 may be arranged separately. Also, the structure of the condensing part 2 may not be limited to the illustrated structure.

In the above embodiments, each heat pipe 3 a, 3 b is formed of the pair of formed plates 31 a, 32 a, 31 b, 32 b. However, it is not always necessary that the heat pipe 3 a, 3 b is formed of two formed plates 31 a, 32 a, 31 b, 32 b.

In the above embodiments, the coupling pipes are formed as separate parts. However, the coupling pipes can be integrally formed with one of the evaporating heat pipe 3 a and the condensing heat pipe 4 a. Further, the above embodiments can be used with any combinations.

Also, the arrangement of the evaporating part 1 and the condensing part 2 is not limited in the exhaust pipe and the engine cooling water passage. Further, the heat recovered in the evaporating part 1 can be used for any other purposes. Also, the use of the heat recovery apparatus is not limited to the vehicle, but may used for other purposes.

The example embodiments of the present invention are described above. However, the present invention is not limited to the above embodiments, but may be implemented in other ways without departing from the spirit of the invention. 

1. A heat recovery apparatus comprising: an evaporating part for performing heat exchange between an internal fluid and a first fluid, thereby to evaporate the internal fluid; and a condensing part for performing heat exchange between the internal fluid evaporated in the evaporating part and a second fluid having a temperature lower than a temperature of the first fluid, thereby to condense the internal fluid, wherein the evaporating part and the condensing part are in communication with each other through a looped passage for circulating the internal fluid therethrough, wherein the evaporating part has a plurality of evaporating heat pipes and evaporating fins, each of the evaporating heat pipes has flange portions projecting from its longitudinal ends in a direction perpendicular to a longitudinal direction of the evaporating heat pipe and each having a tubular shape, the evaporating heat pipes and the evaporating fins are alternately stacked and brazed in a direction perpendicular to the longitudinal direction of the evaporating heat pipes, and the flange portions of the adjacent evaporating heat pipes are coupled to and brazed to each other such that evaporating communication portions are provided by the flange portions and the longitudinal ends of the evaporating heat pipes.
 2. The heat recovery apparatus according to claim 1, wherein each of the evaporating heat pipes is constructed of a first evaporating heat pipe member and a second evaporating heat pipe member each having the flange portions at longitudinal ends thereof, the first and second evaporating heat pipe members are disposed such that the flange portions project in opposite directions, and brazed in a condition arranged between the evaporating fins.
 3. The heat recovery apparatus according to claim 1, wherein the condensing part has a plurality of condensing heat pipes and condensing fins, each of the condensing heat pipes has flange portions projecting from its longitudinal ends in a direction perpendicular to a longitudinal direction of the condensing heat pipe and each having a tubular shape, the condensing heat pipes and the condensing fins are alternately stacked and brazed in a direction perpendicular to a longitudinal direction of the condensing heat pipes, and the flange portions of the adjacent condensing heat pipes are coupled to and brazed to each other such that condensing communication portions are provided by the flange portions and the longitudinal ends of the condensing heat pipes, the heat recovery apparatus further comprising: coupling members coupling the evaporating communication portions and the condensing communication portions, wherein the evaporating part and the condensing part are disposed close to each other.
 4. The heat recovery apparatus according to claim 3, wherein the evaporating part and the condensing part are coupled such that the evaporating heat pipes are disposed parallel to the condensing heat pipes, and at least one of the evaporating communication portions is aligned with one of the condensing communication portions.
 5. The heat recovery apparatus according to claim 3, wherein each of the condensing heat pipes is constructed of a first condensing heat pipe member and a second condensing heat pipe member each having the flange portions at longitudinal ends thereof, and the first and second condensing heat pipe members are disposed such that the flange portions project in opposite directions and brazed in a condition arranged between the condensing fins.
 6. The heat recovery apparatus according to claim 3, wherein each of the coupling members has a pipe shape including stress absorbing portions, and the stress absorbing portions are configured to allow expansion and contraction of the coupling members in a longitudinal direction thereof.
 7. The heat recovery apparatus according to claim 2, wherein the flange portion of one of the first and second evaporating heat pipe members has a stress absorbing portion, and the stress absorbing portion is configured to allow expansion and contraction in a direction perpendicular to the longitudinal direction of the evaporating heat pipe.
 8. The heat recovery apparatus according to claim 7, wherein the stress absorbing portion has a bulge that projects in a radial direction of the flange portion throughout its circumference and allows expansion and contraction in the radial direction.
 9. The heat recovery apparatus according to claim 8, wherein the stress absorbing portion is provided by a bellows portion.
 10. The heat recovery apparatus according to claim 1, wherein the evaporating part is disposed in an exhaust gas passage through which an exhaust gas discharged from an engine flows, the first fluid is the exhaust gas, the condensing part is disposed in a cooling water passage through which an engine cooling water flows, and the second fluid is the engine cooling water.
 11. A heat recovery apparatus comprising: an evaporating part for performing heat exchange between an internal fluid and a first fluid, thereby to evaporate the internal fluid; and a condensing part for performing heat exchange between the internal fluid evaporated in the evaporating part and a second fluid having a temperature lower than a temperature of the first fluid, thereby to condense the internal fluid, wherein the evaporating part and the condensing part are in communication with each other through a looped passage for circulating the internal fluid therethrough, wherein the evaporating part has a plurality of evaporating heat pipes, evaporating fins alternately stacked with the evaporating heat pipes, and communication portions at longitudinal ends of the evaporating heat pipes, the communication portions extend in a direction perpendicular to a longitudinal direction of the evaporating heat pipes and define portions of the looped passage, and the communication portions have bulges for allowing thermal expansion and contraction as stress absorbing members.
 12. The heat recovery apparatus according to claim 11, wherein the condensing part has a plurality of condensing heat pipes, condensing fins alternately stacked with the condensing heat pipes, and communication portions at longitudinal ends of the condensing heat pipes, the heat recovery apparatus further comprising: coupling pipes coupling the communication portions of the evaporating part and the communication portions of the condensing part, wherein the coupling pipes and the communication portions are aligned with each other. 